We performed radionuclide cineangiography at rest and during exercise in 120 patients with coronary artery disease who were not considered candidates for coronary artery bypass surgery because of mild symptoms. Rest or exercise left ventricular ejection fraction were not different between the 99 patients who have remained stable (mean follow-up two years), the 15 patients who have had increased angina requiring operation, and the six patients who have died suddenly. However, the change in ejection fraction from rest to exercise, and the exercise load achieved, identified subgroups with different 2 year event rates. Patients with a decrease in ejection fraction with exercise had significantly worse prognosis than those with an increase in ejection fraction. Among patients with a decrease in ejection fraction during exercise, patients who achieved less than 80 watts work load had a worse prognosis than patients with better exercise tolerance. Thus, the change in ejection fraction from rest to exercise as well as exercise capacity helps to define subgroups at high and at low risk.